Each wind turbine comprises a generator, e.g. a large direct drive generator having a generator stator and a generator rotor for the production of electrical energy.
In order to achieve a relatively high efficiency of a generator, in particular of a generator of a wind turbine, a radial air gap between the rotor elements, e.g. permanent magnets, and the stator elements, e.g. a laminate stack with windings, of the generator should be relatively small, generally in the range of only a few millimeters even for large generators like direct drive or directly driven generators with possibly a diameter of several meters.
To avoid mechanical damage to the rotor and stator elements it is thereby necessary to ensure that the outer surfaces of the rotor elements and the outer surfaces of the stator elements which are arranged oppositely to each other do not come into direct contact with each other during operation of the generator. Consequently the small air gap, which must be of relatively small height due to efficiency reasons, must be guaranteed at a nominal value within narrow tolerances.